A variety of devices are known for centering a drill supported in a drill holder in predetermined relation to the workpiece. See, for example, U.S. Pat. Nos. 441,834, 776,250, 1,647,590, 2,035,999 and 2,328,359. It is common practice to use a seating member, inserted into a slot of a lathe turret and secured to the drill holder, and it is known to accomodate a drill in a 90.degree. V-shaped cutaway formed in the drill holder. Difficulties have been encountered, however, in providing drill holders including such cut-aways which possess the required rigidity to withstand the distorting and deflecting forces arising from the interaction of the drill and the metallic workpiece. The high speed demanded by the tool operation generates rapid vibrations which produce conditions leading the chattering with resulting inaccuracies.
The present invention is directed to overcome the drawbacks of prior art by providing a simple tool holder, e.g. a drill holder, which combines a rigid structure with versatility and adaptablity for tools of different diameters. The invention broadly secures any round stock tool, but for exemplification, reference will be made to drills.
More specifically, the drill holder according to the present invention includes a massive support block of substantially rectangular cross section, with a seating member which is inserted into the slot of a lathe turret and secured to the support block by a hexagonal nut. A hollowed-out portion of the support block has a quasi-cordate cross section in which the apex and the arcuate portion are horizontally related. The apex is disposed a predetermined distance, for most lathes 0.5 or 0.375 inch, above the bottom surface of the drill holder and is at the junction of two substantially straight surfaces which include an angle of 90.degree.. The angle is disposed so as to be bisected by an imaginary horizontal line. An elongated drill, introduced into the hollowed-out portion of the drill holder and positioned in the wedge-shaped space formed by the surfaces including the 90.degree. angle, therefore has the predetermined centerline above the bottom surface of the drill holder. This relation is invariant for drills of any diameter which can be accomodated in the cut-away portion of the drill holder in tangential position relative to the inclined surfaces extending away from the apex of the 90.degree. angle.
A multiplicity of threaded bolts are extended toward the drill in the interior of the support block, at spaced intervals and normal to the drill axis, to secure the drill in its predetermined position with respect to the V-shaped part of the cut-away.
In a preferred embodiment the bottom surface of the drill holder distal to the V-shaped part of the cut-away, is dimensioned so as to be fractionally spaced, e.g. 0.010 inch, from the parallel plane top surface of the lathe turret, so as to enable spring-loading of the drill.